1. Technical Field
The present invention relates to a scanner device, a printing device and a scan method.
2. Related Art
A scanner device for scanning a predetermine scan object (hereinafter, referred to as an “original”) to prepare image data has been known (see JP-A-2004-282561). A carriage of this scanner device has a light source for emitting light. The light emitted from the light source is irradiated onto the original so as to form an irradiation region (hereinafter, referred to as a scan region). The light is reflected from the scan region and is incident to an image sensor. The image sensor stores the reflected light in a predetermined time and converts the stored light into an electrical signal such that image data is generated at a portion of the original according to the scan region which is moved in the predetermined time for storing the reflected light. The carriage is transported in a scan direction by a carriage transporting mechanism using a predetermined motor as a driving source and the scan region is moved along with the carriage.
The scanner device sets a plurality of lines having density corresponding to resolution in the scan direction specified by a user in a scan region of the original. These lines are formed in a band shape and are set parallel to the scan direction. In the scanner device, when the carriage is transported in the scan direction, each line is moved to the scan region. At this time, in the scanner device, the image sensor starts the storage of the reflected light when the scan region reaches a start time of each line and the image sensor finishes the storage of the reflected light when the scan region reaches an end point of each line, such that the image sensor generates image data of the line (hereinafter, referred to as line image data). In this case, in the scanner device, the motor is driven so as to transport the carriage in the scan direction such that a time in which the scan region passes through each line becomes a predetermined time in each line.
When the carriage is driven, a stepping motor is generally used. However, the stepping motor has larger operating sound, compared with a DC motor.
Accordingly, the carriage may be driven by the DC motor. A rotation speed of the motor is controlled by controlling a driving voltage applied to the motor. For example, in order to rotate the DC motor at a very low speed, a very low driving voltage should be applied to the motor. However, since a torque obtained by the driving voltage is smaller than frictional force, a voltage range (dead zone) in which the motor is not rotated occurs. If the motor for transporting the carriage is the DC motor and the very low driving voltage is applied to the DC motor in order to improve reading resolution, the driving voltage may be in the dead zone and thus the DC motor may not be rotated.